#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdbool.h>
 //Definition for singly-linked list.
 struct ListNode {
      int val;
      struct ListNode *next;
};
 
bool hasCycle(struct ListNode* head) {
    struct ListNode* fast, * slow;
    fast = slow = head;
    while (fast && fast->next)
    {
        fast = fast->next->next;
        slow = slow->next;
        if (fast == slow)
            return true;

    }
    return false;
}